repair: handle filesystems with the log in allocation group 0

repair: handle filesystems with the log in allocation group 0

Sindre Skogen reported that repair chokes on a very small filesystem created
by mkfs.xfs from xfsprogs 2.9.4.  It turned out that for some reason this
filesystem had the log in allocation group 0 and thus repairs validation
of the root inode number was off.  Fix this by adding the log blocks if
the log is allocated in allocation group 0.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reported-by: Sindre Skogen <sindre@workzone.no>
Signed-off-by: Christoph Hellwig <hch@lst.de>